The present invention relates to the treatment of biological fluids with sterilizing radiation to inactivate various pathogens, such as viruses, in human plasma. In particular, the present invention relates to a device and method for inactivating pathogens with sterilizing radiation in a continuous flow arrangement while exhibiting radiation dose uniformity.
In the transfusion and infusion medicine field, beneficial fluids are introduced to a patient for therapeutic purposes. Many of these fluids are of biologic origin, such as blood, plasma, or various fractions of blood or plasma. For example, blood plasma protein Factor VIII, which promotes blood coagulation to prevent life threatening bleeding, is used for maintaining hemostasis for hemophilic patients who lack the Factor VIII. Another example is plasma-derived immunoglobulin, which is used for strengthening and supplementing a patient""s immune defense. Contamination of such fluids with donor blood borne pathogens, such as viruses and other microorganisms, can be detrimental to the patient""s health and may even result in death of the patient. Therefore, methods must be set in place to substantially eliminate these pathogens before these fluids are introduced to the patient while minimizing the denaturation of useful fluid components during the pathogen inactivation process.
Existing methods for pathogen inactivation include detergent treatment for inactivating lipid-enveloped viruses, thermal treatment, and chemical and photochemical treatment for rendering various viral agents innocuous. Some of the photochemical treatment methods are described in U.S. Pat. Nos. 5,683,661, 5,854,967, 5,972,593, and the references cited therein. However, these methods tend to be less conducive to high volume and continuous processing applications, such as a production line for the manufacture of Factor VIII or immunoglobulin. These methods are also expensive.
Sterilizing radiation in the form of short ultraviolet (UV) wavelengths, gamma radiation or electron beam (beta) radiation has been found to be effective for inactivation of a broad range of pathogens. The use of a sterilizing radiation process is typically more economical than chemical treatments. Sterilizing radiation is defined as electromagnetic radiation capable of rupturing bonds in the genetic nucleaic acids (DNA) of pathogens. Nucleaic acids are typically much more susceptible to damage by sterilizing radiation than the protein products treated.
U.S. Pat. No. 5,133,932 describes an apparatus for batch treatment of biological fluids with ultraviolet radiation. However, the batch processing method disclosed causes irradiation of the fluids in a spatially uneven manner. Furthermore, the random and chaotic agitation process disclosed causes broad exposure time for various fluid components. This uneven exposure may cause inconsistent radiation dosage, which may result in ineffective pathogen removal (underexposure) or damage to beneficial biological agents (overexposure).
A continuous flow process for the irradiation of biological fluids is more effective than batch processing and is more conducive to high volume production. In a continuous flow process involving a constant sterilizing radiation illumination field, the transit time, or residence time, of the fluid is directly related to the radiation dose received by the fluid. Therefore, a continuous flow treatment process requires that the residence time distribution of the fluid being exposed to the radiation be as uniform as possible. By analogy with the batch process, short residence time distributions lead to an insufficient inactivation dose of radiation and long residence time distributions could lead to damage and reduced potency of beneficial biological agents.
Present continuous flow methods involve fluid flow in a channel. A parabolic velocity profile exists for such fluid flow. In this profile, the fluid at the center of the channel is traveling at maximum velocity and the fluid close to the channel wall remains nearly stationary. Therefore, the residence time is the shortest for the maximum velocity at the center and increases for successive portions of the flow profile moving radially outwardly from the center. In the absence of turbulence or mechanical agitation, the flow volume near the channel walls would have an extremely long residence time. Thus, the flow volume near the channel walls runs the risk of overexposure to the radiation. In addition, if the particular channel wall is on the proximal side of the radiation source, very serious overexposure of the biological fluid can occur.
In addition to residence time distribution, the penetration depth of sterilizing radiation into various biological fluids is also a factor in controlling consistent radiation dosage of the fluid. Depending on the optical density of a particular biological fluid, the penetration of sterilizing radiation into the fluid can be very shallow. This is especially true in the case of low or moderate energy accelerated electrons or short wavelength UV radiation. For example, the penetration of 200 Kev electrons into water is less than 0.5 mm (20 mils). Similarly, UV radiation at 250 nm wavelength loses half of the intensity in human plasma at about a 75 micron (about 3 mils) penetration. Thus, a thin fluid flow path can be advantageous in providing a more uniform radiation dosage to the fluid.
International Application No. PCT/GB97/01454 describes a UV irradiation apparatus that utilizes a static mixer disposed within a cylindrical fluid passage to facilitate mixing of the fluid. The apparatus also incorporates a heat exchanger to control the fluid temperature and prevent localized heating during irradiation. The localized heating purportedly causes the formation of insoluble particles of material. These particles may screen pathogens from the UV radiation, and, therefore, the ""01454 patent application provides a heat exchanger to reduce the likelihood that these particles will form. However, this apparatus focuses on the control of fluid temperature rather than control of residence time distribution of the fluid. The presence of the static mixer increases the flow resistance and has a significant adverse effect on the residence time distribution of the fluid and also significantly increases the pressure head of the fluid flow, thereby making this device less conducive to high volume throughput. Furthermore, the deep channels formed between the screw elements is conducive to non-uniform radiation dosage of the fluid despite the mixing of the fluid. This apparatus does not provide a controlled method for dealing with non-uniform dose exposure due to shallow penetration depth.
These shortcomings in the prior art have created a need for providing a more controlled method for uniform radiation exposure in continuous flow arrangements, particularly for fluids having high optical densities.
It is therefore an object of the present invention to provide a continuous flow device and method that is highly effective in uniformly irradiating high optical density fluids having low radiation penetrations.
It is also an object of the present invention to provide a continuous flow device and method for pathogen inactivation of biological fluids with sterilizing radiation utilizing a thin fluid flow path that promotes a more uniform radiation exposure for fluids having high optical densities.
It is also an object of the present invention to provide a continuous flow device and method utilizing a thin fluid flow path while providing a uniform and narrow residence time distribution of the fluid within the device, thereby providing yet another control over radiation exposure.
It is another object of the present invention to substantially eliminate the development of a velocity profile of the fluid flowing through the device by incorporating a xe2x80x9cconveyingxe2x80x9d mechanism to move the fluid through the device in a controlled manner.
It is another object of the present invention to provide a continuous flow device and method having a minimal air/fluid interface, thereby minimizing protein degradation in the fluid.
It is another object of the present invention to a continuous flow device and method capable of thin film fluid manipulation while minimizing shear stress and shear induced degradation of high protein fluid products.
It is another object of the present invention to provide a continuous flow device and method that is scalable and therefore capable of high volume throughput that is conducive to manufacturing production lines.
It is another object of the present invention to provide a continuous flow device and method that is economical and cost effective.
It is another object of the present invention to provide a continuous flow device and method that is adaptable to various different radiation sources.
It is another object of the present invention to provide a continuous flow device and method that allows for ease of cleaning or provides a disposable fluid path.
It is another object of the present invention to provide a continuous flow device and method that is capable of validation, i.e., demonstration of efficacy, reproducibility and reliability through scientific principles.
These and other objects will be readily apparent after reviewing the description and drawings herein.
The present invention is a device and method for inactivating pathogens in biological fluids with sterilizing radiation in a continuous and thin fluid flow path that exhibits radiation dose uniformity and narrow residence time distribution of the fluid within the device.
In a first embodiment, a thin film fluid path is provided through a thin and relatively flat fluid chamber arrangement. In this device, a relatively flat belt chamber is connected to a fluid flow through an inlet on one end of the belt chamber and an outlet on the other end of the belt chamber. The belt chamber is designed to be disposable. An external pump or other means provides a fluid supply to the device. The belt chamber has a first relatively flat surface and a second relatively flat surface. A radiation permeable plate is disposed adjacent one surface of the belt chamber and is in contact with the belt chamber. A radiation source is provided adjacent a side of the plate opposite the belt chamber. The radiation source provides sterilizing radiation at the optimal wavelengths for the particular fluid. A belt having a plurality of flexible vanes is disposed adjacent the other surface of the belt chamber such that the vanes make contact with the belt chamber. The belt is driven by a roller mechanism in the direction of the fluid flow. As the fluid is introduced into the belt chamber, the flexible vanes provide a squeegee-like action to move the fluid through the belt chamber in discrete packets defined by a pair of vanes. A tension adjuster can be provided to adjust the pressure of the vanes against the belt chamber and plate. As the packets of fluid move through the belt chamber, they are exposed to radiation passing through the high transparency plate.
In a variation of the previously described embodiment, the belt having the flexible vanes is replaced with a belt having a plurality of rotating rigid cylinders. The belt is similarly disposed adjacent the belt chamber such that the cylinders make contact with the belt chamber. The belt is driven by a roller mechanism in the direction of the fluid flow. In this embodiment, as the belt moves the rotation of the rigid cylinders provides a squeegee-like action to move the fluid through the belt chamber in discrete packets defined by a pair of cylinders. A tension adjuster can be provided to adjust the pressure of the rigid cylinders against the belt chamber and the plate. As the packets of fluid move through the belt chamber, they are exposed to radiation passing through the plate.
In another embodiment, a series of rollers having flexible vanes spirally disposed thereon are disposed adjacent to a surface of the belt chamber. The rollers are synchronously driven by a motor and drive mechanism. As the rollers rotate, the spiral vanes push the fluid through the belt chamber. A tension adjuster can be provided to adjust the pressure of the vanes against the belt chamber and plate. As the fluid moves through the belt chamber, they are exposed to radiation passing through the plate.
In yet another embodiment, a narrow belt chamber is positioned parallel to a large roller having a plurality of flexible vanes spirally disposed thereon. The roller is disposed adjacent to and in contact with one surface of the belt chamber and a high transparency plate is disposed adjacent and in contact with the other surface of the belt chamber. A radiation source is provided on a side of the plate opposite the belt chamber. In this configuration, the fluid is moved along through the belt chamber by the spirally configured flexible vanes. The fluid is exposed to radiation passing through the plate as the fluid moves through the belt chamber.
In yet another embodiment, an inner cylinder is concentrically disposed within a hollow radiation permeable outer cylinder having an outer surface and an inner surface. A radiation source is provided around the outside surface of the outer cylinder. A motor rotatably drives the inner cylinder. The inner cylinder has a plurality of flexible vanes angled in a direction opposite that of the direction of rotation. A flexible and relatively flat belt chamber having a fluid inlet and a fluid outlet is disposed between, and in contact with, the inner surface of the outer cylinder and the inner cylinder. A pump provides a fluid supply to the belt chamber. As the fluid is introduced into the belt chamber, the inner cylinder rotates and the flexible vanes provide a squeegee-like action to move the fluid through the belt chamber in discrete packets defined by a pair of vanes. As the packets of fluid move through the belt chamber, they are exposed to radiation passing through the outer cylinder.
In another embodiment, a stationary elongated V-shaped depositor is disposed within a rotating hollow radiation permeable cylinder having an inner surface and an outer surface. A motor rotatably drives the cylinder. A fluid inlet is in fluid communication with the depositor. The depositor deposits a thin film of fluid on the inner surface of the cylinder as the cylinder rotates. The thin film is carried on the inner surface of the cylinder until it reaches a stationary squeegee collector in contact with the inner surface of the cylinder. A radiation source is provided around the outside surface of the cylinder and irradiates the thin film of fluid carried on the inner surface of the cylinder. The squeegee collector is in fluid communication with a fluid outlet. The irradiated fluid exits the device through the fluid outlet. One or more pumps provide a fluid supply to the fluid inlet and from the fluid outlet.
FIG. 1 is a side elevational view of a first embodiment of the present invention that utilizes a belt mechanism having flexible vanes to move a fluid through a chamber being exposed to sterilizing radiation.
FIG. 2 is an assembly view of the basic elements of the first embodiment depicted in FIG. 1.
FIG. 3 is a side elevational view of a second embodiment of the present invention that utilizes a belt mechanism having rotating rigid cylinders to move a fluid through a chamber being exposed to sterilizing radiation.
FIG. 4 is an assembly view of the basic elements of the second embodiment depicted in FIG. 3.
FIG. 5 is an assembly view of the basic elements of a third embodiment of the present invention that utilizes a series of rollers having spirally configured flexible vanes to move a fluid through a chamber being exposed to sterilizing radiation.
FIG. 6 is an assembly view of the basic elements of a fourth embodiment of the present invention that utilizes a single roller having spirally configured flexible vanes positioned parallel to a thin chamber being exposed to sterilizing radiation to move a fluid through the chamber.
FIG. 7 is a perspective view of a fifth embodiment of the present invention that utilizes an inner cylinder having flexible vanes disposed within a hollow outer cylinder to move a fluid through a thin chamber being exposed to sterilizing radiation.
FIG. 8 is a perspective view of a sixth embodiment of the present invention that deposits a thin film of fluid on an inner surface of a rotating cylinder to move the thin film while being exposed to sterilizing radiation.
FIG. 9 is a graph depicting ultraviolet radiation absorptivity of human plasma at 42-fold dilution between 200 nm and 350 nm UV wavelengths.
FIG. 10 is a graph depicting light intensity as a function of penetration depth at absorbances of 20, 40 and 100.